1. Field of the Invention
The present invention generally relates to an image forming apparatus, such as a facsimile and a copying apparatus, and more particularly to an image forming apparatus which has a developing device which removes a residual toner on a photosensitive member to the developing device.
2. Discussion of the Related Art
FIG. 12 shows a conventional image forming apparatus. The apparatus forms an image on a sheet of paper P by devices such as a charging device 100, an exposure device 102, a developing device 104, and a transfer device 106 provided around a photosensitive drum 108 rotating in a direction S. The charging device 100 charges the photosensitive drum 108. The exposure device 102 exposes the charged photosensitive member to form a latent image on the photosensitive drum 108. The developing device 104 includes a toner hopper 131 a feed roller 132, a developing roller 134, a direct-current power source 136, an alternating-current power source 138. The direct-current power source 136 biases a predetermined voltage against alternating-current voltage from the alternating power source 138. The toner contained in the toner hopper 131 is conveyed by the feed roller 132 to the developing roller 134. The developing roller 134 develops the latent image with the conveyed toner to form a developed toner image on the image on the photosensitive drum 108 to the sheet of paper P. In this state, some residual toner remains on the photosensitive drum 108. This residual toner blocks the light from the exposure device 102. In order to overcome this deficiency, the apparatus further includes a discharge device 110 and a distribution roller 112 rotating in a direction U, both of which are located between the transfer device 106 and the charging device 100.
The discharge device 110 includes a discharge charger 114. The discharge charger 114 is coupled to a condenser 116, which, in turn, is coupled to an alternating-current power source 118. Then, the discharge charger 114 discharges onto the photosensitive drum 108 so that the positive and negative charges are balanced. Simultaneously, a mirror 122 reflects light from a discharge lamp 120 onto the photosensitive drum 108. As a result, the charge on the photosensitive drum 108 and the charge of the residual toner are zero. Therefore, the residual toner is not bound to the photosensitive drum 108. In this state, the residual toner remaining on the photosensitive drum 108 arrives at the distribution roller 112, which is coupled to a positive direct-current power source 124. The residual toner comes into sliding contact with the distribution roller 112, which spreads the residual toner across the surface of the photosensitive drum 108. By spreading the residual toner across the surface of the photosensitive drum 108, the distribution roller 112 removes accumulations of residual toner having a thickness that would prevent the light from exposure device 102 from reaching the underlying surface of the photosensitive drum 108 Therefore, the light from the exposure device 102 may reach the entire surface area of the photosensitive drum 108.
However, the conventional apparatus requires two separate structural elements to spread the residual toner on the photosensitive drum 1 (e.g., the discharge device 110 having the charging device 114 coupled to the alternating-current power source 118, and the distributing roller 112 coupled to the direct-current power source 124). Thus, the apparatus becomes bulky and heavy.